The polymerizable organic matrix of dental resins, cements or composites primarily consists of a mixture of monomers, initiator components, stabilizers and pigments (J. Viohl, K. Dermann, D. Quast, S. Venz, Die Chemie zahnärztlicher Füllungskunststoffe [The chemistry of dental filling plastics], Carl Hanser Verlag, Munich-Vienna 1986, 21-27). Mixtures of dimethacrylates are usually used as resins (cf. A. Peutzfeldt, Resin composites in dentistry: the monomer systems, Eur. J. Oral. Sci. 105 (1997) 97-116; J. W. Nicolson, H. M. Anstice, The chemistry of modern dental filling materials, J. Chem Ed. 76 (1999) 1497-1501; J. W. Stansburry, Curing dental resins and composites by photopolymerization, J. Esthet. Dent., 12 (2000) 300-308; N. Moszner, T. Hirt, New Polymer-Chemical Developments in Clinical Dental Polymer Materials: Enamel-Dentin Adhesives and Restorative Composites, J. Polym. Sci. Part A: Polym. Chem. 50 (2012) 4369-4402).
A main disadvantage of the methacrylates used is that their polymerization is accompanied by a volume contraction, so-called polymerization shrinkage. In the case of dental materials, polymerization shrinkage can lead, among other things, to disadvantageous shrinkage stresses and to marginal gap formation in filling composites, to reduced substrate adhesion in fixing composites or coating materials and to impairment of the dimensional stability of prosthesis plastics. In this connection, radically polymerizable cyclic monomers have received much attention in the preparation of dental materials due to the considerably lower polymerization shrinkage compared with linear monomers, such as e.g. methacrylates (cf. R. K. Sadhir, R. M. Luck, Expanding Monomers, CRC Press, Boca Raton etc. 1992).
With respect to other known ring-opening monomers, such as methylene group-containing spiro orthocarbonates (SOCs), spiro orthoesters (SOEs) or bicyclic orthoesters (BOEs), vinylcyclopropanes are characterized by the fact that the vinylcyclopropyl (VCP) group is not sensitive to moisture and that polymers with high molar masses which contain only hydrolytically stable C—C bonds in the main chain are obtained in their radical polymerization. (N. Moszner, F. Zeuner, T. Völkel, V. Rheinberger, Macromol. Chem. Phys. 200 (1999) 2173).
From DE 198 12 888 A1 vinylcyclopropane derivatives and in particular vinylcyclopropane (meth)acrylates are known which can be copolymerized with acrylates and methacrylates.
Moreover, vinylcyclopropanes with several polymerizable groups are known. F. Sanda, T. Takata, T. Endo, Macromolecules 27 (1994) 3986 describe 1-vinyl-5,7-dioxaspiro[2.5]octan-6-one, a hybrid monomer which contains a vinylcyclopropane group and a cyclic carbonate group, and T. Okazaki, F. Sanda, T. Endo, Macromolecules 28 (1995) 6026 describe 1,10-bis(vinyl)-4,8,12,15-tetraoxatrispiro[2.2.2.2.2.2]pentadecane, a monomer in which two vinylcyclopropane groups are joined to each other via a hydrolysis-sensitive spiroacetal unit. Compared with monofunctional vinylcyclopropanes, these compounds do not have any improved radical copolymerizability with (meth)acrylic compounds.
EP 0 798 286 A1 relates to multifunctional vinylcyclopropane derivatives with two to six vinylcyclopropane groups which enable the preparation of crosslinked polymers.
Using the example of the radical copolymerization of 1,1-bis(ethoxycarbonyl)-2-vinylcyclopropane with methyl methacrylate (MMA), it could be shown (F. Sanda, T. Takata, T. Endo, Macromolecules, 27 (1994) 3982) that compared with methacrylates, vinylcyclopropanes are characterized by a lower radical polymerization capability, which considerably restricts their practical use. It is particularly disadvantageous that the known 1,1-bis(alkoxycarbonyl)-2-vinylcyclopropanes which are easy to obtain have a low photopolymerization activity.
EP 1 413 569 A1 discloses dental materials based on bicyclic cyclopropane derivatives, such as e.g. 2-[bicyclo[3.1.0]hex-1-yl]-acrylic acid methyl ester, which exhibit an improved reactivity on radical polymerization (N. Moszner, F. Zeuner, U.K. Fischer, V. Rheinberger, A. de Meijere, V. Bagutski, Macromol. Rapid. Commun. 24 (2003) 269). However, these more reactive monofunctional bicyclic cyclopropyl acrylates can only be obtained with great difficulty.